ABSTRACT Legal recreational cannabis became available in Nevada on July 1st, 2017. As states legalize adult recreational cannabis use, policymakers must regulate a new industry with little science to inform their decisions. A central question emerging from this process is how, if at all, cannabis legalization affects adolescent cannabis use, and the role of dispensary availability or advertising density in adolescent consumption. Population studies have yielded conflicting results, showing both increases and no change in adolescent cannabis use following adult recreational legalization, often depending on adolescents' age, a state's type of cannabis policy, or the specific cannabis use outcome used in analysis. This proposal presents research to advance our understanding of how legalization of adult cannabis use affects adolescent cannabis use by capitalizing on a natural experiment opportunity in Nevada and assessing potential mechanisms driving change such as cannabis dispensary and outdoor advertising density. We propose three aims. The first aim uses 2017 and 2019 Nevada and New Mexico Youth Risk Behavior Survey (YRBS) data in a difference-in-difference analysis to compare change in cannabis use behaviors in Nevada to change in cannabis use behaviors in New Mexico, where recreational cannabis use is illegal. Next, we will use 2017 and 2019 Nevada YRBS data to detail within-state patterns in adolescent cannabis use and unique outcomes rarely examined in adolescents, such as preferred mode of administration (e.g., smoked, vaped, eaten) and vehicular risk behavior (e.g., driving while high). Finally, we propose primary collection of geospatial and image data to examine how cannabis dispensary and outdoor advertising density affect adolescent cannabis use behaviors. Importantly, analyses will include both high school and middle school students, which have rarely been included in prior studies of the effect of legalization on adolescent cannabis use behavior. The timing of this application is ideal, as geodata and advertising image will align with the data collection period for the 2019 NV YRBS. UNR undergraduate, master's, and doctoral students will be integrally involved in data collection, analysis, presentation, and publication. The proposed research will not only contribute to our understanding of how recreational cannabis laws affect adolescent use, but will also help build a critical mass of student and faculty capacity in cannabis research in support of future NIH grant proposals from UNR.